Question First: after hours of research, I can’t seem to find a straightforward consensus about whether this is a great idea or a horrible plan. Can’t even figure out if open cell is better than closed! Is there no consensus on this? Is it too new?

Context: I live in New York state (climate zone 5) and have a hip roof with a short attic. We have mini-split heat pumps for heat and air that run through the attic.

We got a new roof (including sheathing/decking) less than a year ago only to find black mold on the underside because the roofer didn’t add enough venting (powered vent fan, but not enough soffit vents). I also know that there are TONS of air leaks and not nearly enough insulation in my attic floor.

Keeping my roof/attic vented like it is, I’m looking at: mold spraying, air sealing, soffit work, added insulation. Based on initial quotes and conversations, $15k-$20k.

Then I spoke with two separate insulation contractors who both recommended converting to a hot roof, conditioned attic rather than vented using open cell spray foam on the roof decking. One quote was $10k for the whole foam job (R38 everywhere). They even said we could spray this right over the black mold to stop it’s growth.

One guy mentioned that it’s acceptable according to NYS code (https://up.codes/viewer/new_york/ny-residential-code-2010/chapter/11/energy-efficiency#11). I found this section but I can’t quite decide what it means:

4. In Climate Zones 5 and 6, any air-impermeable (eg., spray foam) insulation shall be a Class III vapor retarder, or shall have a vapor retarder coating or covering in direct contact with the underside of the insulation.

5.Either Item 5.1, 5.2 or 5.3 shall be met, depending on the air permeability of the insulation directly under the structural roof sheathing.

5.1Air-impermeable (eg., spray foam) insulation only. Insulation shall be applied in direct contact with the underside of the structural roof sheathing.

5.2Air-permeable (eg., fiberglass or cellulose) insulation only. In addition to the air-permeable installed directly below the structural sheathing, rigid board sheet insulation shall be installed directly above the structural roof sheathing as specified in Table R1102.2.1.1 for condensation control.

5.3Air-impermeable and air-permeable insulation. The air-impermeable (eg., spray foam) insulation shall be applied in direct contact with the underside of the structural roof sheathing as specified in Table R1102.2.1.1 for condensation control. The air-permeable (eg., fiberglass or cellulose) insulation shall be installed directly under the air-impermeable (eg., spray foam) insulation.